This project investigates the role of free radical reactions in cellular injury caused by mineral particles and metal ions. The following major findings were obtained: (A) tetrandrine, a benzylisoquinoline alkaloid, used in China as an antifibrotic drug to treat human silicosis, is an antioxidant in cellular systems. Phorbol 12-myristate 13-acetate (PMA)- induced nuclear factor (NF)-kappaB activation involves free radical reaction. Tetrandrine efficiently inhibits the PMA-induced NF-kappaB activation via scavenging free radicals. The results indicate that tetrandrine functions as an antioxidant in a cellular system. Since NF- kappaB regulates protooncogenes, including c-myc, tetrandrine may inhibit silica-induced carcinogenesis via inhibition of c-myc overexpression. (B) Cr(VI) is capable of inducing NF-kappaB activation in Jurkat cells (CD4+ human lymphoblast cell line). Reduction of Cr(VI) to a lower oxidation state is required for Cr(VI)-induced NF-kapppaB activation. *OH radicals generated by a Cr(IV)-mediated Fenton-like reaction play a dominant role. Chromium chelation may be used to prevent or attenuate Cr(VI)-induced NF-kappaB activation. (C) Direct low frequency electron spin resonance (ESR) was used to detect and identify the paramagnetic metal intermediate and reactive free radical generation. It was demonstrated in whole living mice that reduction of Cr(VI) generates Cr(V), identified to be Cr(V)-NAD(P)H complex. The reactive free radical, SO3*-, was detected and identified using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap. A new field of studies on free radical reactions in whole living animals becomes feasible using this method.